It is known that with such circuits, an energy transfer takes place from the primary side of the circuit to the secondary side of the circuit. In particular, the transfer from the primary side to the secondary side of the circuit occurs via the barrier by means of a converter, in particular a transformer, which induces a voltage or a current on the secondary side by means of an electromagnetic coupling. It is thus possible to supply the secondary side via the barrier.
In order to determine the illuminant current passing through the illuminant, or the illuminant line, which can be used to regulate the brightness of the illuminant, it is known to carry out a determination of the illuminant current on the secondary side. This is disclosed, for example, in WO 2014/060899. It is furthermore known that, as is shown by way of example in FIG. 1, a control circuit SE activates, directly or indirectly, a switch unit S having a clocked switch, e.g. via a drive unit.
The switch unit S can have, for example, a single clocked switch, or numerous clocked switches. Thus, the switch unit S can comprise, in particular, an inverter having a high-side switch, and low-side switch in comparison thereto.
Starting from the switch unit S, a converter winding L2_1 (inductivity coil) is then supplied. This converter winding L2_1 can be a component of an LLC circuit thereby, and be fed from a midpoint of the inverter. In particular, a converter (e.g. resonance converter, LLC converter) is thus fed, from which the secondary side of the circuit is fed by means of an electromagnetic coupling of the primary side-converter winding L2_1 and the secondary side-converter windings L2_2, L2_3 (shown here as separate windings L2_2, L2_3, coupled magnetically) via a barrier B.
LED terminals LED+ and LED− are supplied with a DC voltage, smoothed out via a smoothing capacitor C2, via the diodes D1 and D2, which form a rectifier, in order to operate the illuminant.
An auxiliary winding Lh is provided with a measurement circuit E on the secondary side of the circuit, wherein the auxiliary winding Lh is coupled electromagnetically with the primary side winding L2_1. The measurement circuit E then measures, by means of the auxiliary winding Lh, a current induced on the secondary side of the circuit, or records a parameter reflecting it. The corresponding parameter reflecting the current is determined thereby through the measurement circuit E, and returned to the control unit SE via the barrier B, via a bypass element X, which can be an optocoupler or another transformer. The control unit SE can then evaluate the parameter as the actual value of the current passing through the illuminant, and use it for regulating the illuminant. In doing so, the control unit SE can compare, in particular, the actual value for the current with a target value, and activate the switch unit S accordingly.
The circuit depicted in FIG. 1 has, in this regard, the disadvantage that, for one thing, the measurement circuit E must be provided on the secondary side of the circuit, and that furthermore, a bypass element X is required for bypassing the barrier B, which leads to relatively high circuit costs and complicated circuit assemblies.